The goals of this research program are to further elucidate the in vivo and in vitro functions of E. coli exonuclease VII and single-strand DNA binding protein. We propose to study the cellular control of the production of exonuclease VII. It is hoped that this information will allow us to isolate a strain of E. coli which produces increased amounts of the enzyme. Such a strain will serve as a general source of exonuclease VII both for our own in vitro studies as well as a source to others. The elucidation of the cellular control of the production of exonuclease VII may serve as a general model for the control of other nucleic acid enzymes, e.g., DNA polymerase III. For this reason we propose to study the cellular control of the production of DNA polymerase III. We will purify exonuclease VII to homogeneity, determine its subunit structure and initiate further in vitro biochemical studies of the homogeneous enzyme. We will extend our studies of the role of exonuclease VII in DNA repair. Finally, the amino acid sequence of E. coli single-strand binding protein from wild type and mutant strains will be determined. This will aid in elucidating the structure-function relationship between DNA binding protein and nucleic acids.